[ObjC ARC] Converts ios/web:ios_web_inttests to ARC.

ios/web/browser_state_web_view_partition_inttest.mm

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <WebKit/WebKit.h>
 
 #include <memory>
 #include <string>
 
 #include "base/mac/foundation_util.h"
@@ skipping 70 matching lines @@
     id result = web::ExecuteJavaScript(web_view, @"document.cookie");
     return base::mac::ObjCCastStrict<NSString>(result);
   }
 
   // Sets a localstorage key, value pair on |web_view|.
   void SetLocalStorageItem(NSString* key,
                            NSString* value,
                            WKWebView* web_view) {
     NSString* set_local_storage_item = [NSString
         stringWithFormat:@"localStorage.setItem('%@', '%@')", key, value];
-    NSError* unused_error = nil;
+    __unsafe_unretained NSError* unused_error = nil;
     web::ExecuteJavaScript(web_view, set_local_storage_item, &unused_error);
   }
 
   // Returns the localstorage value associated with |key| from |web_view|.
   id GetLocalStorageItem(NSString* key, WKWebView* web_view) {
     NSString* get_local_storage_value =
         [NSString stringWithFormat:@"localStorage.getItem('%@');", key];
     return web::ExecuteJavaScript(web_view, get_local_storage_value);
   }
 
@@ skipping 72 matching lines @@
   SetLocalStorageItem(@"someKey2", @"someValue2", web_view_2);
   // Due to platform limitation, it's not possible to actually set localStorage
   // item on an OTR BrowserState. Therefore, it's not possible to verify that a
   // localStorage item has been correctly set.
   // Look at
   // http://stackoverflow.com/questions/14555347/html5-localstorage-error-with-safari-quota-exceeded-err-dom-exception-22-an
   // for more details.
   // Test that LocalStorage has not leaked over to |web_view_1|.
   EXPECT_NSEQ([NSNull null], GetLocalStorageItem(@"someKey2", web_view_1));
 }